Space Studies Find Line Across Pacific Linked to Currents

By WALTER SULLIVAN

Published: October 25, 1994

OBSERVATIONS from space shuttles and other vehicles have shown a remarkable, clearly visible line that marches for hundreds of miles across the Pacific Ocean as if the waters were being divided.

Scientists are not invoking a miracle to explain the strange phenomenon, but the line is nevertheless a wonder of nature. They attribute the dark green line, which is several hundred yards wide, to an abundance of microscopic plants that thrive where cold, nutrient-rich water welling up from polar seas meets warm equatorial currents. The explosion of life from this encounter feeds much of the ocean.

Westward-moving waves delineating this encounter have been traced across more than 4,000 miles of the Pacific from the vicinity of the Galapagos Islands in the east to an area south of Hawaii.

On the surface, this produces a series of wave fronts, spaced about 600 miles apart, that move west 30 miles a day. This meeting of hot and cold water masses has been observed in whitecaps, narrow bands of rich biomass and sharp changes in water surface temperature.

The observations, described in the current issue of Nature, showed enormous production of the microscopic sea creatures known as diatoms. They formed a narrow band of very dark green water, "a distinct line in the sea" visible for hundreds of miles.

It has long been known that such equatorial encounters generate abundant life, producing diatom deposits as much as three miles thick, but never before has such an eruption of marine life been so extensively observed on the surface.

Reached yesterday by telephone, one of the experimenters, Dr. Pierre Flament of the University of Hawaii in Honolulu, said that for many years hints of such a line had been reported by mariners. Some had thought the discoloration marked a midocean reef. What was new, he said, was the line's documentation by diverse observations, showing it only 100 yards in width. Because it produces surface turbulence he said it was hoped the space shuttle radar would ultimately be able to trace it across most of the ocean.

The diatom lines seem to be an ancient phenomenon. From cores of sediment extracted from the equatorial sea floor, scientists in the Ocean Drilling Program have found that from 15 million to 4.4 million years ago there were bursts of ocean productivity far greater than even the most striking current instances.

Over the millennia the periods of high productivity, followed by sudden mortality, produced showers of diatom shells forming layers and a "chalk line" on the sea floor.

As the Pacific floor drifted northwest, this chalk line, having been formed at the Equator, became buried in sediment, but drilling has reached it, confirming such motion over the past 150 million years. Although the chalk line originated at the Equator, it has been found so close to the volcanic islands of Japan that traces of Japanese eruptions are found with the chalk.

In 1926, the naturalist Charles William Beebe reported that at "the meeting place of the great ocean currents" east of the Galapagos he had observed a "concentration of organisms greater than I have ever seen." Their microscopic forms were so abundant that in places the sea was like soup.

The new observations of interaction between the cold South Equatorial Current and the warm North Equatorial Countercurrent included measurements of sea surface temperature. These were made from the NOAA-11 weather satellite and with NASA's P-3 research aircraft flying 500 feet above the water. The P-3 also measured the amount of plant chlorophyll by illuminating the water with a laser that made it fluoresce. This showed a band of great abundance about 10 miles wide near 1.8 degrees North Latitude.

Measurements of ocean currents made from the research vessel Thompson of the University of Washington, found a mile-wide front where a slab of cold water 230 feet feet thick was diving under a 130-foot slab of warm water. Near the surface patches of buoyant diatoms were observed; they seemed to be doubling their population daily. During the season of maximum current intensity, in summer and autumn, the patches and resulting breaking waves were visible from space.

Authors of the report in Nature were Dr. James A. Yoder of the University of Rhode Island, Dr. Steven A. Ackleson of the Office of Naval Research, Dr. Richard T. Barber of Duke University, Dr. William M. Balch of the Rosensteil School of Marine and Atmospheric Science in Miami and Dr. Flament. Findings on Leg 138 of the Ocean Drilling Program and on earlier legs were described in that program's Proceedings by Dr. Alan E. S. Kemp and Dr. Richard B. Pearce of the University of Southampton in England and Dr. Jack G. Baldauf of Texas A & M University.

Photo: A line across part of the Pacific Ocean, filmed from the space shuttle Atlantis in 1992, where microscopic plants grow between two currents. (NASA)